1. Field of the Invention
The invention is a control valve for use in controlling the raise rate and the lowering rate of a draft control cylinder in an agricultural tractor hitch system. The valve is a closed center valve.
2. Description of the Prior Art
The closed center draft control valve presented in this specification is designed for use in a pressure and flow compensated draft control system. The draft control valve is based on the prior art open center draft control valve body that included similar but operationally different components. The prior art valve would not operate in the pressure and flow compensated environment that the instant invention is designed to operate in. Furthermore, the principles of operation of the newly developed and herein presented closed center draft control valve and the prior art open center draft control valve are completely different.
It is expected that there are hydraulic systems in the extensive array of prior art devices that show spool valves, pilot operated poppet valves and manual poppet valves in various assemblages. However, the inventor of the system presented herein is not aware of the existence of a prior art valve that utilizes the components of this invention in an assembly having the operating characteristics and advantages of this invention.
It is amongst the objects of this invention to provide a closed center draft control valve that can closely meter flow of hydraulic fluid from a variable displacement pump to a draft control cylinder through a valve spool that can be feathered.
It is also an object of this invention to provide a closed center draft control valve that can closely meter the evacuation of fluid from a draft control cylinder.
Another advantage of this draft control valve is that it eliminates the necessity of a pump and an unloading valve in a draft control system. This thereby reduces cost of the draft control system and reduces the number of necessary assemblies.
Another object of the invention is to have return flow exhausted from the draft control cylinder not be controlled by the spool valve that is used to direct fluid to the draft control cylinder thus saving cost through decreased complexity of the draft control valve body.
Also an object of this invention is to provide a fine control of the rate of fluid being exhausted through the use of pilot valve and feathering through the use of a pilot controlled poppet valve.